Lumbar spinal stenosis (LSS) is a narrowing of the spinal canal. Though LSS
may occasionally occur congenitally with symptoms presenting in the thirties
and forties, by far the largest number of patients with LSS acquire the disease
later in life and are over 60 years of age. The spinal canal is narrowed as
a result of degenerative changes. It is estimated that as many as 400,000 Americans
may suffer from this disease the majority of which have not been diagnosed.
The treatment is a decompressive lumbar laminectomy.

Anatomy

The lumbar spine and pelvis, the low back, supports the entire body. The lumbar spine allows bending forward and backward and to twist at the waist

The normal lumbar spine is composed of five building blocks called vertebrae that sit on the sacrum, which is the back part of the pelvic bone. (Figure 1)

Each vertebra is constructed of a body, lamina, and pedicles, which surround an opening, the spinal canal.(Figure 2)

A spinous process extends posteriorly (towards the back) from the lamina in the midline. Through the spinal canal pass the nerve roots that emerge from the end of the spinal cord and go to form the nerves to the legs. (Figure 3)

Each root exits the spinal canal through a 'hole' in the side of the canal formed by two adjacent vertebrae called a foramen

The roots float in fluid and are contained within a fibrous sac called the dura

Separating any two vertebral bodies is a soft elastic material called a disk. The disk is composed of two parts, a soft center called the nucleus and a tough outer band called the annulus. (Figure 4). There are five lumbar disks

On each side of the back of the spinal canal and linking one vertebra to the next are a series of small joints called facets

Figure
1 - The lumbar spine is composed of five vertebra separated by disks.

Figure
2 - Cross-section of a lumbar vertebrae showing the various parts.

Figure 3 - Cross-section showing the spinal
canal and nerve roots.

Figure 4 - Cross-section showing
a disk.

Pathology

With advancing age, several changes occur in the bone, disk, joints and
ligaments of the lumbar spine. (Figure 5)

Bones. The bones tend to loose water and become less dense (spondylosis).
Because of degenerative changes near the disk margins, an overgrowth
of bone may occur producing bony spurs (osteophytes) that may encroach
on the exiting foramina with compression of the enclosed nerve roots

Disk. The disks also loose water and compress thus narrowing the disk
space. The spacing between the vertebrae likewise narrows resulting
in further narrowing of the foramina

Joints. Along with the other degenerative changes, there develops
a degenerative arthritis of the facet joints that causes the joints
to enlarge. Sometimes the lining of the joint (synovium) enlarges or
becomes cystic. This combination of events results in narrowing of the
spinal canal and increasing stiffness of the spine. If the joints degenerate
such that the fibrous capsule loosens, then one vertebrae may slip over
the one below causing further narrowing of the canal and instability

Ligaments. With advancing age the ligaments tend to stretch and thicken.
This further encroaches on the spinal canal and foramina

The above combination of changes results in nerve roots being compressed
within the spinal canal or as the roots exit from the spinal canal through
the foramina

Figure 5 - Cross-section of the lumbar spine
showing stenosis caused by an overgrowth of the facets and thickening
of the ligaments.

Click image above to view animation

History and Exam

Individuals with spinal stenosis may complain of:

Back pain. A fairly constant complaint is lower back pain. The pain
is usually described as dull or aching but occasionally the pain may
be sharp and severe

Nerve root pain. Irritation or compression of the nerve roots in the
lumbar spinal canal or foramina produce this pain. (All the roots together
in the lumbar spinal canal are called the cauda equinae.) The pain may
begin in the low back and go to the buttocks, thighs and down the legs.
In most cases the pain goes to both sides but in many sufferers the
pain is only on one side

Numbness and tingling or pins and needles feeling. This is type of
discomfort is also caused by irritation or compression of the nerve
roots

Loss of bowel or bladder function. This is caused by severe compression
of the cauda equinae

Pain on standing or walking (neurogenic claudication). This is the
most classic symptom of LSS

The deep aching pain begins when standing or walking. Frequently the
patient complains of not being able to walk to the mailbox or around
the block

The patient may find relief by bending forward at the waist while
walking, thus the patient may be seen leaning forward on a shopping
cart in the grocery or mall

Sitting down relieves the pain. This may be mistaken for a similar
pain on walking but due to narrowing of the arteries going to the legs
(vascular claudication)

On examination, the physician may find few abnormalities

The reflexes on tapping the knee or ankle may be depressed

There may be a mild weakness of the legs

The response to pin or touch may be less than normal

The pulses in the legs are normal

Tests

Special tests are necessary in making the correct diagnosis. These are:

X-ray of the lumbar spine. The x-rays may show collapse of the disk spaces
with narrowing of the foramina, bony spurs, scoliosis, slippage of one vertebrae
over another (spondylolesthesis) and degenerative changes in the facet joints

CT (computerized tomography) scan. This test images the lumbar spine by
X-ray as a series of cross-sections. The changes in the bone and joints
can be evaluated as to the degree of spinal canal narrowing

MRI (magnetic resonance imaging) scan. This test images the lumbar spine
though the use of a magnetic field and radar waves. The soft tissues such
as the ligaments are imaged better than bone. This test also can be used
to determine the degree of narrowing (Figure 6A,B)

Lumbar myelogram. This test involves the injection of an X-ray contrast
material containing iodine into the fluid that surrounds the cauda equinae.
Regular X-rays as well as a CT scan are then obtained. This test usually
gives the clearest picture of the degree of spinal narrowing and the number
of spinal levels involved (Figure 7)

Pain and anti-inflammatory medication such as aspirin, ibuprofen, acetaminophen
and naproxen may be of benefit particularly in early cases of LSS

Physical therapy. Exercises for strengthening and stretching the back
and abdominal muscles may help

Epidural cortisone injection. Cortisone is injected into the spine between
the bone and the dura. This sometimes may reduce inflammation and reduce
pain. Injections of steroids should be used cautiously since any long term
series of injections can have adverse side effects

Indications

Surgery is indicated when:

Pain medication and physical therapy do not help

The back and leg pain is severe enough to limit an individuals everyday
activities or quality of life

There is a neurologic deficit such as weakness in the legs, loss of sensation
in the legs or loss of bowel or bladder control

There is significant pain on walking

The tests confirm the diagnosis of LSS

Surgical Procedure

Decompressive lumbar laminectomy is the procedure most commonly carried
out for LSS. The procedure is carried out in the following manner:

The number of vertebra that are involved is determined and an incision
is made extending from one vertebrae above to one vertebrae below the vertebra
to be operated upon

The muscles are elevated off of the spinous processes and lamina of the
vertebra and held apart with an instrument called a retractor

The spinous processes and lamina of the involved vertebra are then carefully
removed under magnification (magnification loupes or operating microscope).

These structures are removed using an air or electrically driven burr
and small bone biting instruments called rongeurs (Figure 8)

Using the same instruments, the overgrowth of the facet joints and the
bone pushing in on the foramina are removed as necessary

The overgrown and stretched ligaments are also removed

All bleeding is stopped and the wound is sutured

Figure 8 - Cross-section of the lumbar spine showing removal
of the lamina and the return of the dural sac to normal.

Other procedures

Some surgeons may prefer to perform multiple partial
laminectomies instead of the more extensive complete laminectomy

In this case, only the lower one-half of the lamina and ligaments
are removed on each side of the involved vertebra

Using the same instruments, the overgrowth of the facet joints and
the bone pushing in on the foramina are also removed as necessary

The overgrown and stretched ligaments are also removed

This may preserve the stability of the involved structures

Unilateral decompressive laminectomy

Used In cases in which the pain and bone overgrowth are unilateral
(one sided) (Figure 9)

A laminectomy is carried out on the side of the overgrowth. The lamina
above and below the narrowing may be partially or completely removed

An important part of the procedure is the removal of the medial (towards
the midline) portion of the overgrown facet, the part that traps the
nerve root

Bilateral decompressive laminectomy through a unilateral approach

This minimally invasive procedure uses an endoscope or operating microscope
for improved visualization and approaches the stenosis from one side
thus minimizing trauma to the back muscles

A partial laminectomy of the involved vertebra is performed on the
side on which the patient has the more severe symptoms

The overgrowth of the facet joints and the bone pushing in on the
foramina are also removed as necessary

The lower part of the spinous process is removed to allow access to
the opposite side

Most or all of the lower half of the lamina of the opposite side is
then removed followed by the overgrown ligaments (Figure 10)

Spinal fusion

In a few individuals with LSS, there is an associated spinal instability
because of destruction of the facet joints. In these cases it is necessary
to add a fusion to the procedure

Decompressive laminectomy alone is not an indication for fusion. If
there is instability, there will be a noticeable shift in alignment
of one vertebra over the one below (spondylolesthesis) on flexion and
extension X-rays of the lumbar spine

Fusion is not indicated in elderly patients with only a small shift

A second opinion is warranted if spinal fusion is being considered
in addition to the decompressive laminectomy

The fusion is accomplished through the same incision

Bone taken from the iliac crest (hip bone) is used for the fusion.
The bone is laid down lateral to the pedicles and over the transverse
processes. If there is considerable instability, the addition of screws
and rods may be necessary

Figure 10b - (Right) Similar CT scan after decompressive
laminectomy through a right unilateral approach showing relief of the
stenosis (arrowheads).

Complications

While decompressive laminectomy is a relatively safe procedure. Despite even
the greatest care, complications do occur.

Hemorrhage. Hemorrhage may cause compression of the nerve roots with resulting
weakness or paralysis in the legs, loss of feeling and loss of bowel or
bladder control

Tearing of the dura over the nerve roots. This problem occurs because
the ligaments may be stuck to the dura, and can lead to injury to the nerve
roots, pain, and leakage of cerebrospinal fluid (the fluid that surrounds
the nerve roots). If leakage occurs, this must be corrected to prevent later
infection

Infection of the wound

Direct injury to the nerve roots causing weakness or paralysis in the
legs, loss of feeling and loss of bowel or bladder control. Tears in the
dura and injury to the nerve roots are minimized by the use of magnification
at the time of surgery

Deep venous thrombosis with pulmonary embolism. This is a very serious
problem. In some patients, blood clots will form in the veins of the legs
or pelvis. These clots may come loose from the vein wall and travel to the
lungs causing severe difficulty with respiration and even death

Since this surgery is most often performed on an older population, the
patient may also be subject to complications related to to heart or lung
disease, diabetes, or hypertension

After Surgery Care

After surgery the patient is given instructions for care at home until
seen in the doctor's office

The doctor should be contacted if there is any:

Redness or discharge from the wound

Fever

Weakness or numbness in the legs or

Trouble with urination

Most patients are discharged from hospital on the first or second post-operative
day

Elderly patients with heart, lung, kidney or other diseases such as diabetes
may require additional hospital stay